.left,.top,.right{
    float: left;
    background: #cccccc;
    width: 300px;
    height: 200px;
}
.clearfix:before,
.clearfix:after{
    content: "";
    display: block;
    clear: both;
}
@media (max-width: 600px) {
    .left,.top,.right{
        width: 500px;
        height: 400px;
    }
}